The present invention relates to polyalkoxyamines obtained from xcex2-substituted nitroxides, which may be used especially as free-radical polymerization initiators.
Recent developments in controlled free-radical polymerization have revealed the value of polyalkoxyamines as described in Accounts of Chemical Research, 1997, 30, pages 373-382.
These polyalkoxyamines, under the action of heat, in the presence of an olefin which may undergo free-radical polymerization, initiate the polymerization while at the same time allowing it to be controlled.
The mechanism for this control may be represented diagrammatically as below: 
with M representing a polymerizable olefin and P representing the growing polymer chain.
The key to the control is associated with the constants Kdeact, kact and kp (T. Fukuda and A. Goto, Macromolxc3xa9cules 1999, 32, pages 618 to 623). If the ratio kdeact/kact is too high, the polymerization is blocked, whereas when the ratio kp/kdeact is too high, when the ratio kdeac/kact is too low though, the polymerization is uncontrolled.
It has been found (P. Tordo et al., Polym. Prep. 1997, 38, pages 729 and 730; and C. J. Hawker et al., Polym. mater. Sci. Eng., 1999, 80, pages 90 and 91) that xcex2-substituted alkoxyamines make it possible to initiate and control efficiently the polymerization of several types of monomers, whereas TEMPO-based alkoxyamines [such as (2xe2x80x2,2xe2x80x2,6xe2x80x2,6xe2x80x2-tetramethyl-1xe2x80x2-piperidyloxy-)methylbenzene mentioned in Macromolecules 1996, 29, pages 5245-5254] control only the polymerizations of styrene derivatives.
The Applicant has now found that, starting with polyoxyamines of the general formula (I): 
in which nxe2x89xa72,
A represents a polyfunctional core and RL represents a radical with a molar mass of greater than 15, A and RL will be defined more fully later, it can synthesize polymers and copolymers with well defined architecture.
Starting with a dialkoxyamine of formula. (I) in which n=2, it is possible to synthesize triblock copolymers, each block being derived from monomers as different as alkyl acrylates and/or styrene derivatives, with excellent control of the polymerization and the polydispersity and with very short polymerization reaction times.
Thus, for example, it is possible to polymerize successively 2 monomers M1 and M2: 
By way of example, M1=alkyl acrylate and M2=styrene.
Starting from a trialkoxyamine, xe2x80x9cstar-shapedxe2x80x9d polymers will be obtained.
One subject of the invention is thus polyalkoxyamines of general formula (I): 
in which: nxe2x89xa72,
A represents a divalent or polyvalent structure which may be chosen from the structures given below in a nonlimiting manner: 
in which R1 and R2, which may be identical or different, represent a linear or branched alkyl radical containing a number of carbon atoms ranging from 1 to 10, phenyl or thienyl radicals optionally substituted with a halogen atom such as F, Cl or Br, or a linear or branched alkyl radical containing a number of carbon atoms ranging from 1 to 4, or alternatively with nitro, alkoxy, aryloxy, carbonyl or carboxyl radicals; a benzyl radical, a cycloalkyl radical containing a number of carbon atoms ranging from 3 to 12, a radical comprising one or more unsaturations; B represents a linear or branched alkylene radical containing a number of carbon atoms ranging from 1 to 20; m is an integer ranging from 1 to 10; 
in which R3 and R4, which may be identical or different, represent aryl, pyridyl, furyl or thienyl radicals optionally substituted with a halogen atom such as F, Cl or Br, or with a linear or branched alkyl radical containing a number of carbon atoms ranging from 1 to 4, or alternatively with nitro, alkoxy, aryloxy, carbonyl or carboxyl radicals; D represents a linear or branched alkylene radical containing a number of carbon atoms ranging from 1 to 6, a phenylene radical or a cycloalkylene radical; p ranging from 0 to 10; 
in which R5, R6 and R7, which may be identical or different, have the same meanings as R1 and R2 of formula (II), q, r and s are integers ranging from 1 to 5; 
in which R8 has the same meaning as R3 and R4 of formula (III), t is an integer ranging from 1 to 4, u is xe2x89xa72 and xe2x89xa66; 
in which R9 has the same meaning as the radical R8 of formula (V) and v is xe2x89xa72 and xe2x89xa66; 
in which R10, R11 and R12, which may be identical or different, represent a phenyl radical, optionally substituted with a halogen atom such as Cl or Br, or with a linear or branched alkyl radical containing a number of carbon atoms ranging from 1 to 10; W represents an oxygen, sulfur or selenium atom, and w is equal to zero or 1; 
in which R13 has the same meaning as R1 of formula (II), and R14 has the same meaning as R3 or R4 of formula (III); 
in which R15 and R16, which may be identical or different, represent a hydrogen atom, a linear or branched alkyl radical containing a number of carbon atoms ranging from 1 to 10, or an aryl radical, optionally substituted with a halogen atom or a hetero atom,
RL has a molar mass of greater than 15; the monovalent radical RL is said to be in a xcex2 position relative to the nitrogen atom, the remaining valencies on the carbon atom and on the nitrogen atom in formula (1) may be linked to various radicals such as a hydrogen atom, a hydrocarbon-based radical, for instance an alkyl, aryl or aralkyl radical containing from 1 to 10 carbon atoms, the carbon atom and the nitrogen atom in formula (1) may also be linked together via a divalent radical so as to form a ring; preferably, however, the remaining valencies on the carbon atom and on the nitrogen atom of formula (I) are linked to monovalent radicals; preferably, the radical RL has a molar mass of greater than 30, the radical RL may have, for example, a molar mass of between 40 and 450; by way of example, the radical RL may be a radical comprising a phosphoryl group, said radical RL preferably being represented by the formula: 
in which R17 and R18, which may be identical or different, may be chosen from alkyl, cycloalkyl, alkoxy, aryloxy, aryl, aralkyloxy, perfluoroalkyl and aralkyl radicals and may contain from 1 to 20 carbon atoms; R17 and/or R18 may also be a halogen atom, for instance a chlorine or bromine or fluorine or iodine atom; the radical RL may also comprise at least one aromatic ring such as the phenyl radical or naphthyl radical, said radical possibly being substituted, for example with an alkyl radical containing from 1 to 10 carbon atoms.
According to the present invention, the monovalent radicals linked to the carbon atom bearing the radical RL, which may be identical or different, may be a hydrogen atom, a linear or branched alkyl radical containing a number of carbon atoms ranging from 1 to 12, a phenyl radical, or an aralkyl radical containing, for example, from 1 to 10 carbon atoms. By way of illustration of such monovalent radicals, mention will be made of ethyl, butyl, tert-butyl and isopropyl radicals.
According to the present invention, the alkoxyamines of formula (I) in which n=2 and in which at least one of the remaining valencies on the carbon atom bearing RL is linked to a hydrogen atom, are most particularly preferred.
The two remaining valencies on the carbon atom may also be linked to a divalent radical so as to form a ring including the carbon atom bearing the radical RL, said ring possibly containing a number of carbon atoms ranging from 3 to 10 and possibly containing a hetero atom such as N, O or S.
The remaining valency on the nitrogen atom may also be linked to a group xe2x80x94C(CH3)2Z with Z=xe2x80x94COOalkyl, xe2x80x94COOH, xe2x80x94CH3, xe2x80x94CN, xe2x80x94CH2OH, xe2x80x94CH2OSi(CH3)3.
The polyalkoxyamines of formula (I) may be prepared according to methods known in the literature. The method most commonly used involves the coupling of a carbon-based radical with a nitroxide radical. The coupling may be performed using a halo derivative A(X)n in the presence of an organometallic system, for instance CuX/ligand (X=Cl or Br) according to a reaction of ATRA (Atom Transfer Radical Addition) type as described by D. Greszta et al. in Macromolecules 1996, 29, 7661-7670.
This method consists in transferring an atom or a group of atoms to another molecule in the presence of an organometallic system CuX/ligand in a solvent medium, according to the scheme: 
One procedure which is generally used consists in dissolving the organometallic system such as CuBr/ligand in an organic solvent which is preferably aromatic, such as benzene or toluene, and then in introducing into the solution the compound A(X)n and the xcex2-substituted nitroxide 
As examples of ligands used, mention will be made of bipyridine, 4,4xe2x80x2-bis(5-nonyl)-2,2xe2x80x2-bipyridine and tris(2-pyridylmethyl)amine (TPA).
The reaction mixture is then stirred at a temperature between 20xc2x0 C. and 90xc2x0 C. for a period which may be up to 48 hours, or even more.
Next, the precipitate is filtered off, rinsed with a solvent such as ether and the filtrate is then washed with an aqueous solution containing 5% by weight of CuSO4 and then finally with water. The resulting solution is dried over magnesium sulfate and the solvents are then evaporated off under reduced pressure.
According to another particular advantageous procedure, a metal salt MX such as CuX, a ligand, the compound A(X)n and the xcex2-substituted nitroxide: 
are mixed together with stirring in an organic solvent, in a xcex2-substituted nitroxide/A(X)n molar ratio ranging from n to 2n, the reaction medium is kept stirring at a temperature of between 20xc2x0 C. and 90xc2x0 C. until the xcex2-substituted nitroxide has disappeared, the organic phase is recovered and washed with water, and the polyalkoxyamine (I) is then isolated by evaporating off the organic solvent under reduced pressure.
As examples of ligands which may be used according to this procedure, mention will be made of:
tris[2-(dimethylamino)ethyl]amine: 
N,N,Nxe2x80x2,Nxe2x80x2,Nxe2x80x3-pentamethyldiethylenetriamine (PMDETA): 
N,N,Nxe2x80x2,Nxe2x80x2-tetramethylethylenediamine:
(CH3)2xe2x80x94Nxe2x80x94CH2CH2xe2x80x94Nxe2x80x94"Parenopenst"CH3)2xe2x80x2
1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA): 
cyclic polyamines such as:
1,4,7-trimethyl-1,4,7-triazacyclononane,
1,5,9-trimethyl-1,5,9-triazacyclododecane,
1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane.
PMDETA will preferably be used.
The oxidation state of the active species of metal M of the metal salt is equal to 1 (MI).
This active species may be added as is to the reaction medium, preferably in the form of a metal halide such as CuBr.
The active species may also be generated in situ according to the redox reaction:
MIIX+M0⇄2MIX
using a metal salt MIIX such as CuBr2 in which the metal M is in oxidation state 2 (MII) and the same metal in oxidation state zero (M0).
A metal salt MX in which the metal M is in oxidation state 1 (MIA) and the same metal M in oxidation state 0 (M0) may also be introduced into the reaction medium.
According to this procedure, the ligand is used in a ligand/MI molar ratio ranging from 1 to 5 and preferably ranging from 1 to 2.
The xcex2-substituted nitroxide/A(X)n molar ratio ranges from n to 1.4n and preferably is in the region of 1.
As illustrations of xcex2-substituted nitroxides 
which may be used according to the present invention, mention will be made of:
N-tert-butyl-1-phenyl-2-methylpropyl nitroxide,
N-(2-hydroxymethylpropyl)-1-phenyl-2-methylpropyl nitroxide),
N-tert-butyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide,
N-tert-butyl-1-dibenzylphosphono-2,2-dimethylpropyl nitroxide,
N-tert-butyl-1-bis(2,2,2-trifluoroethyl)phosphono-2,2-dimethylpropyl nitroxide,
N-tert-butyl[(1-diethylphosphono)-2-methylpropyl]nitroxide,
N-(1-methylethyl)-1-cyclohexyl-1-(diethylphosphono)nitroxide,
N-(1-phenylbenzyl)[(1-diethylphosphono)-1-methyethyl]nitroxide,
N-phenyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide,
N-phenyl-1-diethylphosphono-1-methylethyl nitroxide,
N-(1-phenyl-2-methylpropyl)-1-diethylphosphonomethylethyl nitroxide.
Most of the intermediate compounds A(X)n in which X represents a chlorine atom or a bromine atom, and which are capable of generating free radicals, are products that are either commercially available or are obtained according to methods described in the literature.
The compounds such as those represented by formula (IVi): 
are novel compounds and, as such, form part of the present invention.
In this formula, R5, R6 and R7, which may be identical or different, represent a linear or branched alkyl radical containing a number of carbon atoms ranging from 1 to 10, a phenyl radical, a benzyl radical, a cycloalkyl radical containing a number of carbon atoms ranging from 3 to 12, and q, r and s are integers ranging from 1 to 5.
The compounds of formula (IVi) according to the present invention were prepared according to a method which consists in introducing an acid bromide of formula (XI): 
(R5, R6 or R7)
with a 1,3,5-tris(xcex1-hydroxyalkyl)cyanuric acid in an acid bromide/cyanuric acid derivative molar ratio which is substantially equal to 3, in heating the reaction medium at a temperature between 50xc2x0 C. and 100xc2x0 C., which is maintained for about 12 hours. After cooling to room temperature, the reaction medium is taken up in a halogenated solvent such as CH2Cl2 and washed with water till neutral.
The resulting solution is dried over MgSO4 and the solvent is removed under reduced pressure.
The compounds obtained are identified by mass spectrometry and by 1H and 13NMR.
The polyalkoxyamines of formula (I) according to the present invention may be used for the polymerization and copolymerization of any monomer containing a carbon-carbon double bond, which is capable of undergoing free-radical polymerization. The polymerization or copolymerization is performed under the usual conditions known to those skilled in the art, taking into account the monomer(s) under consideration. Thus, the polymerization or copolymerization may be performed in bulk, in solution, in emulsion or in suspension, at temperatures ranging from 50xc2x0 C. to 250xc2x0 C. and preferably ranging from 70xc2x0 C. to 150xc2x0 C. As nonlimiting examples of monomers which may be used according to the present invention, mention will be made of vinylaromatic monomers such as styrene, substituted styrenes, dienes, acrylic monomers such as alkyl or aryl acrylates and methacrylates, optionally containing fluorine, for instance methyl acrylate, butyl acrylate or methyl methacrylate, and acrylamides such as N,N-dimethylacrylamide. The monomer may also be vinyl chloride, vinylidene difluoride or acrylonitrile.
The nitroxidexe2x80x94optionally corresponding to the polyalkoxyamine (I) usedxe2x80x94may optionally be added to the polymerization medium, in a nitroxide/polyalkoxyamine (I) molar ratio ranging from 0.01n % to 20n % preferably ranging from n % to 10n %.
The polyalkoxyamines (I) according to the present invention may also be used for the synthesis of xe2x80x9csequencedxe2x80x9d block copolymers according to a procedure which consists in carrying out, in a first step, the bulk, solution, suspension or emulsion polymerization of a monomer M1 or a mixture of monomers containing a carbon-carbon double bond capable of undergoing free-radical polymerization in the presence of a polyalkoxyamine (I) at a temperature ranging from 50xc2x0 C. to 250xc2x0 C. and preferably ranging from 70xc2x0 C. to 150xc2x0 C., and then, in a second step, allowing the temperature to fall and optionally evaporating off the residual monomer(s), and then, in a third step, in introducing the monomer M2 or a new mixture of monomers into the reaction medium obtained above, and then resuming the polymerization by simply raising the temperature.
By way of example, sequenced block copolymers such as polystyrene-polybutyl polyacrylate-polystyrene (PS-BUA-PS) may be prepared in this manner.
The examples which follow illustrate the invention.
The compounds obtained in the synthesis examples are identified by CHN microanalysis and by 1H, 13C and 31P NMR.
The xcex2-substituted nitroxide used has the formula: 
and will be denoted as DEPN.
It was obtained by oxidation of diethyl 2,2-dimethyl-1-(1,1-dimethylethylamino)propylphosphonate using meta-chloroperbenzoic acid according to a protocol described in International patent application WO 96/24620.
The general reaction used in Examples 1 to 9 is as follows: 
The polynitrogen ligands used are:
N,N,Nxe2x80x2,Nxe2x80x2,Nxe2x80x3-pentamethyldiethylenetriamine, denoted hereinbelow as PMDETA,
tris(2-pyridylmethyl)amine, denoted hereinbelow as TPA,
bipyridine, denoted hereinbelow as BIPY.
A-(X)n denotes a polyfunctional core comprising n halo functions. We used polybromo or polychloro esters, except in Example 7 in which the following chloro phosphite was used: 
and in Example 8 in which para-bis(1-bromoethyl)benzene was used, obtained according to a conventional method by reacting diethylbenzene with two equivalents of N-bromosuccinimide.
In order to obtain chloro esters of Examples 3, 4 and 9, we used the following standard reaction: 
by directly reproducing the procedures known to those skilled in the art.
The bromo esters of Examples 1 and 2 are obtained in accordance with Example 251 of International patentapplication WO 98/40415.
The tribromo triester used in Example 5 is obtained by reacting 1,3,5-tris(2-hydroxyethyl)cyanuric acid with 2-bromopropionyl bromide and is described in Example 5.
The alkoxyamines A1 and A2 are those containing sequences of acrylate-DEPN type. Those denoted by a name of the type S1, S2, S3 or S4 contain sequences of phenylethyl-DEPN type.